1. Field of the Invention
The invention pertains to the field of optical displays. More particularly, the invention pertains to apparatus and methods for enhancement of a real image projection system.
2. Description of Related Art
The present invention pertains to a real image projection system and, in particular, to such a system in which an image of a real object is formed in space, giving the illusion that a real object exists at that point in space, when in reality it does not.
Visual display systems typically use a curved reflector with a beamsplitter positioned at a 45 degree angle to the curved reflector""s optical axis, to divert the input beampath at a 90 degree angle to the viewing axis or imaging beampath. This method has been used since the early 1950s for flight simulation, and commonly is referred to as the WAC window system. These systems typically are used in an on-axis configuration, meaning that the optical axis, or the un-tilted curved reflector""s center of radius, is located along the viewing axis. When viewing such an on-axis system, any object within the viewing area images within the system.
One of the earliest working real image displays is depicted in White""s 1934 publication of xe2x80x9cFundamentals of Opticsxe2x80x9d. It shows a spherical mirror positioned behind a table. A flower vase is mounted below the table and a real image of the vase is projected sitting on the table-top. In the late 1980""s, real image display systems were further developed, typically consisting of two on-axis parabolic reflector segments, as shown in U.S. Pat. No. 4,802,750. In the early 1990""s, similar systems were built that use a beamsplitter having high reflection and low transmission, in order to reduce ghosting effects. By 1999, a system was developed using a circularly-polarized window in an on-axis, WAC window-style configuration. For example, U.S. Pat. No. 6,163,408 was issued in 2000. Later, a tilted system was developed, using an off-axis, curved reflector, as disclosed in International Patent Application No. PCT/US00/11234 and PCT Publication No. WO 00/65844. That system comprises a curved reflector tilted at an angle between 5 and 20 degrees from the viewing axis. A beamsplitter is positioned along the viewing axis, tilted at 45 degrees to the curved reflector""s axis. This is a significant improvement because it eliminates ghost imaging completely; the system no longer requires a 42% transmission circular polarizer to eliminate ghosting. A 70% transmissive front window is instead used to provide a system transmission of 15%.
With the availability of such high transmission real imaging systems, many new enhancements are possible that were not available previously. One invention that enhances a real image system is a device that is referred to hereinafter as a xe2x80x9cphoto-screenxe2x80x9d device. The device is basically a printed, partially transparent material, which can be incorporated as a front window for a real image projection system. The photo-screen invention is used in a manner roughly similar to but significantly different from that of a scrim. In the interest of avoiding doubt, the term scrim is used herein to describe a material having a weave pattern or perforated pattern, wherein about 50% of the surface is open or transparent and 50% is solid or non-transparent. The scrim typically is used as a projection screen, and also on bus windows to display advertisements, while still allowing light to pass through the windows to the inside of the bus.
A scrim is employed in the imaging system disclosed in U.S. Pat. No. 5,291,297. The patent discloses a perforated scrim located behind a beamsplitter, facing inward toward the display, and not visible to the viewer. The scrim is used as a projection screen, with the image emanating from inside the system, and a virtual image of the scrim photograph is formed and visible behind the CRT face. The image on the scrim is not viewed directly, and the system is not used for a real imaging system.
U.S. Pat. No. 5,257,130 discloses a scrim window in a real image projection system, however the scrim is used to project an image on the face of a cloth-like woven material at the window opening. However, the scrim of the ""130 patent is significantly different in structure and method of use than the present xe2x80x9cphoto-screenxe2x80x9d invention described herein. For example, the system disclosed in the ""130 patent requires an external light source to be positioned at an oblique angle to the scrim and projected onto the surface of the scrim. In contrast, the present photo-screen invention uses only the ambient light available within the room.
The device disclosed in the ""130 patent is used as a diffuser and projection screen, and requires a directed external light source or projector to illuminate the scrim, as described in the specification and claimed in claims one through seven. The device is based on a weave configuration and is limited to a hole pattern density of between five and fifteen points per inch, as recited in claim 12. In contrast, the present photo-screen invention does not use holes, but instead uses a clear dot pattern and has a density of between 25 and 50 points per inch. The reason for the higher density is to increase the resolution of the real image, virtually eliminating the xe2x80x9cdottedxe2x80x9d appearance from light passing through the dot pattern.
Another significant advantage of the present invention is improved visibility of the background image in a well-lighted room. When used as a projection screen, the scrim of the ""130 patent would require subdued lighting conditions to minimize washing out of the image from ambient lighting.
The scrim of the ""130 patent, because of its construction method of woven thread, has significant limitations as to the ratio of transmission to reflection. The scrim of the ""130 patent is also limited to a cloth or thread material and cannot be constructed onto a rigid substrate.
The printing process used to prepare the photo-screen of the present invention can be performed on any clear substrate, including glass. Perhaps one of the clearest differences between the present photo-screen invention and the scrim disclosed in the ""130 patent is that the scrim of the ""130 patent does not constitute a printed material. Rather, the image is projected onto the scrim using an external projection source. There is no teaching in the prior art of printed graphics applied to the surface of a scrim. Indeed, the woven thread pattern of the scrim would make printing on the surface thereof effectively an impossible task, and because of the coarse nature of the scrim, there would be very little detail visible in the printed image.
Briefly stated, a photo-screen device for a real image projection system includes a transparent or semi-transparent material having a fixed or static image applied to the surface thereof, wherein the photo-screen is positioned so as to intersect a real image beampath of the real image projection device.
In an alternative embodiment, a method for producing a photo-screen device for a real image projection system includes the steps of printing colors thereon in reverse order and positioning the photo-screen such that the non-printed side faces a viewer of the real image.